1. Technical Field
2. Description of the Related Art
Organic thin films have been extensively investigated to realize different kind of devices in many application fields such as sensors, actuators and electronic circuit components; in particular, organic semiconductors, have been used as active layer in organic thin film transistors (OTFT), in RF-ID, large-area flexible displays, in optoelectronic devices such as organic light emitting diodes (OLED) and organic solar cells. Moreover, in the interest to produce biomimetic devices many electromechanically active materials, i.e., materials changing their shape when subjected to an input signal or producing an output signal when subjected to force or bending, have been studied. Among these kind of “smart materials”, electroactive polymers (EAP) have been extensively investigated and used to realize electromechanical devices with sensing and actuating capabilities. Among EAPs, ionic polymer metal composites and conducting polymers have been largely investigated to realize biomimetic sensors actuators and artificial muscles. Ionic polymer metal composites (IPMCs) generally consist of a thin polymeric membrane having a thickness of about 200 μm, coated, generally through an electroplating process, with noble metal electrodes, generally platinum, with a thickness of 5-10 μm. When a voltage is applied to these electrodes, the IPMC bends, while, when a displacement is applied a voltage is measured from the electrodes.
U.S. Pat. No. 6,475,639, entitled “Ionic Polymer Sensors and Actuators”, of Shahinpoor et al. describes methods of making the same for applications requiring sensing, actuating and displacement control. In this case the devices are realized by using the IPMC that are polymer metal composites, therefore the devices are characterized by a metallic coating of the membrane, forming at least one electrode.
Malone et al. [1,2] explored the possibility to use IPMC and Conducting polymers as active materials to freeform fabricate actuators. They synthesized strips of CP actuators trough electropolymerization from a liquid electrolyte containing the monomer, by growing the polymer film starting from their dispersion. In particular, polypyrrole (Sigma-Aldrich), and of PEDOT/PSS (Sigma-Aldrich) dispersion in liquid electrolyte were investigated. Moreover in order to obtain air-operable actuators, they used either a “solid polymer electrolyte” (SPE) which contains some liquid to allow ion migration, or a liquid electrolyte surrounded by some kind of encapsulation.
On another account, thin-film and printed batteries with their customizable shapes, flexible form factors and ultra-low weight are enabling new functionality to be added to a broad range of electronic products, such as smart cards, RFID and sensors both increasing their usefulness and the size of their addressable markets.
For these reasons many companies are investing in printable batteries and photovoltaic research. Varta has developed a 3 V extremely flat lithium-polymer primary cell for use in smart cards. It is embedded in a plastic card with thickness of 0.4 mm and provides a capacity of 25 mAh. Solycore. Inc. has also developed an ultra-thin flexible lithium-polymer battery (Flexion), giving a nominal voltage of 3 V and a capacity of 10 mAh up to 50 mAh and a thickness of 0.37 mm-0.45 mm.